xcex1-Alumina powder having a particle size of less than 60 nanometers is produced from hydrated alumina.
Alumina powders are used as polishing material in the manufacture of oxidized ceramics and silicone chips. The particle size of such powders has been decreasing from micrometer level to submicrometer level, and, lately, to nanometer level. At the nanometer level, as the interval between crystallites is reduced, the quantum dispersion during calcining is tighter. In addressing the issue, T. G. Langdon, Ceramic. Inter., Vol. 19, 279-286, 1993, indicated the temperature required for enhancing calcination rate and reducing sintering, which eventually expanded the scope of application to ceramics. Despite this, in manufacturing nanometer xcex1-alumina, chemical co-precipitated alumina powder invariably sinters together in the calcination stage, making it impossible to obtain even finer superfine xcex1-alumina.
Taiwan patents related to manufacturing superfine xcex1-alumina powder are indexed under APIPA, including: U.S. Pat. No. 246,668, Submicrometer boehmite gel liquid; U.S. Pat. No. 175,369, Manufacturing process of xcex1-Alumina from Alumina gel; and U.S. Pat. No. 4,169,883, Process for Preparing Ultra-stable High Surface Area Alpha-Alumina. In the most prevalent practice of using a chemical solvent to produce xcex1-alumina, boehmite is the most common precursor. During heat treatment final stability is achieved through phase conversion. In recent years superfine polishing powders used for integrated circuits are primarily xcex1-alumina. The need for even finer micro-particle polishing abrasives is due to the micro-development of products. For xcex1-alumina as polishing material, the requirement is even finer than present production capability. This means that manufacturing nanometer grade abrasives is a key technology in the micro-development of integrated circuits.
High-sheer mixing boehmite with surfactant forms a micro-micelle, which is calcined at about 1,050xc2x0 C. for approximately 30 minutes to produce xcex1-alumina. The product is a black net-like fragile substance, residual carbon of which is burnt off after cooling to a temperature between 800xc2x0 C. and room temperature. After deagglomeration treatment and centrifugal settling in a suitable liquid, xcex1-alumina having a particle size of less than 60 nm is obtained.